Drawing apparatus and method

ABSTRACT

APPARATUS FOR DRAWING ARTICLE FROM BLANKS WHICH CONTRAIN NO EXCESS MATERIAL, COMPRISES A PUNCH, DRAW RING, AND INNER AND OUTER PRESSURE PADS. THE OUTER PRESSURE PAD HOLDS THE BLANK DURING THE INITIAL STAGE OF THE DRAWING PROCESS. THE INNER PRESSURE PAD IS APPLIED TO THE ARTICLE AFTER SUCH INITIAL STAGE AND INCLUDES A PRESSURE SURFACE HAVING A SHAPE MATING WITH THE DRAW RADIUS OF THE ARTICLE FORMED DURING THE PROCESS.

Feb. 23, 1971 PFANNER L 3,564,895

DRAWING APPARATUS AND METHOD Filed Oct. 18, 1968 INVENTORS GUNTHER E.PFANNER GEORGE A. BOHMANN 7L 5 'AT TORNEYS United States Patent3,564,895 DRAWING APPARATUS AND METHOD Gunther E. Pfanner, Huntington,and George A. Bohmann, New Hyde Park, N.Y., assignors to FairchildHiller Corporation, Farmingdale, N.Y., a corporation of Maryland FiledOct. 18, 1968, Ser. No. 768,826 Int. Cl. B21d 24/08 US. Cl. 72-351 4Claims ABSTRACT OF THE DISCLOSURE Apparatus for drawing article fromblanks which contain no excess material, comprises a punch, draw ring,and inner and outer pressure pads. The outer pressure pad holds theblank during the initial stage of the drawing process. The innerpressure pad is applied to the article after such initial stage andincludes a pressure surface having a shape mating with the draw radiusof the article formed during the process.

This invention relates to apparatus for hot-drawing materials where itis highly desirable to employ a minimum blank size.

There is considerable evidence indicating that titanium would be ahighly desirable material from which to fabricate helmets for militarypurposes. From a practical viewpoint with regard to mass productionconsiderations, a hot-forming process is preferable to a cold-formingone. Consequently, it has been proposed to employ a hotdrawing apparatusfor the purpose of manufacturing titanium helmets. However, prior arthot-drawing techniques unavoidably produce a substantial amount of wastematerial. This is not a serious matter when working with relativelyinexpensive metals such as steel and aluminum, but in the case of a moreexpensive metal such as titanium (or beryllium) this question of wasteis important since, in the case of helmets, the waste which must beultimately trimmed to form the finished article may comprise as much astwenty percent of the entire blank.

Accordingly, the main object of the present invention is to provideapparatus which can be used for drawing articles, where substantiallythe entire blank is formed to the desired shape and there is virtuallyno leftover waste material.

Briefly, in accordance with the invention, apparatus for drawingarticles includes a heated punch, draw ring, and inner and outerpressure pads for retaining a blank during the process. The outerpressure pad is applied to the blank to be drawn during the initialphase of the process and the inner pressure pad is applied during thefinal stage. The surface of the inner pad which contacts the blank isshaped to mate with the draw radius of the article formed during theprocess whereby it is unnecessary to include a special flange or otherexcess portion of the blank to hold the blank during the process.

The invention is described in further detail below with reference to theattached drawings, wherein:

FIG. 1 is a side sectional view of a preferred embodiment of theinvention; and

FIGS. 2A to 2D are diagrammatic illustrations showing the differentsteps in a drawing process according to the invention.

The apparatus according to a preferred embodiment of the invention isshown in FIG. 1 prior to drawing an elliptical blank to form, forexample, a helmet. The apparatus includes a heated cylindrical punch 12the dome of which is shaped to correspond to the desired shape of thehelmet and a draw ring 14, which is also heated, extending downwardlyfrom a fixed support member 16.

3,564,895 Patented Feb. 23, 1971 Punch 12 is hydraulically operated bystandard means (not shown) to draw the blank 10 into the draw ring 14.

Blank 10 is restrained during the process by an annular outer pressurepad 18 and an annular inner pressure pad 20 positioned between the outerpad 18 and punch 12. The inner pressure pad 20 is made flexible byradial slots 21 suitably milled through its bottom and inner surfaces.The means (not shown) are provided to heat the inner and outer pressurepads.

The outer pressure pad 18 rests on a circular base plate 22 which iscoupled by actuator rods 24 to respective hydraulic cylinders 26 so thatthe pad 18 can be urged against the blank 10 and bottom portion of drawring 14. Outer pad 18 may be movable within a cylindrical guide 27. Theinner pressure pad 20 is mounted on a plurality (e.g. eight) of basesegments 29 each of which is mounted on top of the interior end of arespective lever 30. Each lever 30 is pinned at 32 to a pair of lugs 34extending upwardly from the base plate 22. The outer ends of the levers30 are connected to respective actuator rods 36 which are controlled byhydraulic cylinders 38 supported on separate L-shaped brackets 40secured to the the bottom of base plate 22. This arrangement removes thecylinders 38 from the heated portions of the apparatus. Actuation of theflexible inner pressure pad 20 by independent hydraulic systems enablesvariable control of the peripheral restraining force applied to theblank. This assures an even draw and, if desired, can assist in shapingthe finished article by changing the rate of feeding the blank. Thecontinuous slotted pad 20 (as opposed to a segmented one) produces aneven graduation in the forces applied by areas of pad 20 in whichadjacent base segments 29 are applying different forces.

The inner lip 42 of the draw ring 14 is formed to a radius of curvatureR which defines the draw radius of the article formed during theprocess. The corresponding upper surface 44 of inner pressure pad 20,which is the surface which contacts blank 10, is shaped to a matingradius of curvature R which is slightly greater than R to account forthe presence of blank 10 between the pad 20 and draw ring 14. This is animportant feature of the invention, as will become more apparent belowduring the description of the drawing process.

Punch 12, draw ring 14 and pressure pads 18 and 20 may all be heated bymeans of conventional cartridge type heaters embedded therein. Thetemperature of each of the individual components may be controlledseparately and automatically by means of thermocouples suitably embeddedin the respective parts. The means and criteria for controlling thetemperature of these parts will be known by those skilled in the art.Preferably, the punch temperature will be maintained several hundreddegrees lower than the temperature of the draw ring to aid in reducingthinout.

The drawing sequence as applied by the apparatus of FIG. 1 isillustrated in FIGS. 2A to 2D. In FIG. 2A, the blank 10 is placed inposition between the punch 12 and draw ring 14. The outer pressure pad18 is actuated to hold the blank 10 against draw ring 14 (FIG. 2B), andthen punch 12 is actuated to initiate a partial draw of the blank 10into the draw ring 14.

When the blank 10 has been drawn sufiiciently to form the draw radius R(FIG. 2C) the segments of the inner pressure pads are then actuated bythe hydraulic cylinders 38 thereby clamping the blank 10 against thesimilarly shaped inner lip 42 of draw ring 14. The process is thencompleted (FIG. 2D) by fully extending the punch 12 through draw ring 14during which the edges of the blank 10 will be pulled from between theouter pressure pad 18 and draw ring 14. However, since the edges ofblank 10 will still be retained by the segments of the inner pressurepad 20, the draw can be completed. Because the segments of the innerpressure pad are contoured to correspond to the draw radius of thearticle formed during the drawing process, the blank can be retainedagainst the draw ring 14 until the entire edge has been pulled past theinnermost point of contact of the pressure pad 20. Actually, in the caseof a helmet as shown in FIG. 2D where it is desirable to include aslight flange, it is not necessary to draw the edge beyond the innerpressure pad.

There are various ways in which the movement of the inner pressure pad20 can be synchronized with the position of the punch relative to thedraw ring. Preferably, the sequence is programmed to occur as a singlesmooth draw controlled, for example, by cams which are actuated by themovement of the punch.

Obviously, the invention has utility regardless of the nature of thedrawn article. Its main advantage is in permitting the use of minimumsize blanks such that no trimming of excess material is required afterdrawing. This not only reduces the cost of material but also reduces theprocessing costs (by avoiding the trimming and related steps) andincreases the percentage of deformation due to drawing rather thanstretching, thereby minimizing thin-out.

What is claimed is:

1. Apparatus for drawing an article, including a draw ring, a punchadapted to push a blank into said draw ring, and an outer pressure padfor holding the edge of the blank at least during the initial drawingoperation, the improvement comprising an inner flexible pressure padbetween said punch and outer pressure pad for holding said blank atleast during the terminal portion of the drawing operation, a surface ofsaid inner pressure pad being adapted to contact said blank underpressure, said surface being shaped to mate substantially with the drawradius of the blank when it is drawn by said punch into said draw ring,and means for applying dilferential pressures to circumferentiallyspaced portions of said inner pressure pad, the inner pressure pad beingsufficiently flexible to provide a substantially non-incrementalvariation in pressure between circumferentially displaced regions ofsaid inner pressure pad when different forces are applied to saidcircumferentially spaced regions.

2. Apparatus according to claim 1, wherein said inner pressure padcomprises a continuous ring having a plurality of radially extendingslots.

3. Apparatus according to claim 2, wherein said slots do not extendthrough the surface of said inner pressure pad adapted to contact saidblank.

4. Apparatus according to claim 3, wherein said means for applyingdifferential pressures comprises a plurality of segments contactingrespective portions of a surface of said inner pressure pad oppositesaid first named surface and means for applying substantiallyindependent forces to said segments. 7

References Cited UNITED STATES PATENTS 3,420,089 1/1969 Myers 72-351FOREIGN PATENTS 480,594 8/1929 Germany 72-350 280,900 5/1952 Switzerland72351 RICHARD J. HERBST, Primary Examiner

